fix compilation without mesh module

Common/GmshMessage.cpp

Fltk/onelabWindow.cpp

Geo/GFace.cpp

Geo/GFaceCompound.cpp

Geo/GFaceCompound.h

Geo/GModel.cpp

Geo/GModelVertexArrays.cpp

Graphics/drawGeom.cpp

Graphics/drawMesh.cpp

Graphics/drawPost.cpp

Mesh/BackgroundMesh.cpp

Mesh/BackgroundMesh.h

Mesh/CMakeLists.txt

Mesh/meshGFaceLloyd.cpp

Mesh/meshPartitionOptions.cpp

Mesh/meshPartitionOptions.h

Numeric/DivideAndConquer.cpp

Plugin/Distance.cpp

Plugin/ExtractEdges.cpp

Post/PViewDataListIO.cpp